Hirtenberger Patronen Since 1857 - BaroneRosso.it

Fuel Draw Problems? We have found in some instances, modelers using the VT 49 were unable to obtainsufficient fuel draw.This is usually caused by insufficient oil content or the type of oil used in the fuel. The rotary valve requires anoil film to develop the necessary seal. Add about 4 ounces of castor oil to 1 gallon of fuel to correct the problem.Also try a different brand of fuel.If still, after break-in and use of the above remedy, you experience inadequate fuel draw when the aircraft isheld in a upward position, hook up the muffler pressure line direct to the fuel tank and vent both breathernipples to open air via a piece of fuel line to the bottom of the fuselage. You must use the correct fuel oil contentas indicated with this hook up.Return Your Warranty Card. You receive many benefits by returning your warranty card. Your standard 90 daywarranty will be extended to two years just by sending in the warranty card. If we don't have your warranty cardon file we cannot help you under our warranty. Sorry, NO EXCEPTIONS to this policy.READ EVERYTHING FIRST! THEN START YOUR ENGINE.STARTING AND BREAK-INAll HP engines are produced to the highest standards and inspected before leaving the factory, but they are not"BROKEN-IN" and will require approximately 90 minutes of running before the full potential of the engine isrealized. Break-in can be accomplished by airborne or bench running.A model engine makes sounds that will tell you how it's performing. Four cycle engines make sounds that are alot more subtle than a two cycle engine, you'll have to listen very carefully for them, recognize their message,and make adjustments to the fuel control needle valves accordingly. The mixture of fuel and air is controlled bythe amount of fuel metered by the needle valve.RICH MIXTURE running is characterized by a slower, sometimes irregular, sputtering exhaust sound. Theexhaust gas will be smoky and probably contain small droplets of oil. This condition is good for Break-in sincethe engine receives excess lubrication and runs cooler.SLIGHTLY RICH type setting is fast enough to pull the airplane but is still too rich to achieve full RPM's. This isthe setting you normally look for before launching the airplane because the engine will run leaner whenairborne.PEAKED RUNNING is obtained as the main needle is closed (clockwise), this reduces the amount of fuelmixed with the air drawn into the engine. At a specific point, which varies with each engine, air temperature,altitude and relative humidity, the exhaust note will change into a smooth, steady note. If the needle is closedfurther, the note will stay smooth, but will weaken. The peak occurs just at the break point from a rich settingand further leaning will ruin the engine. A lean setting raises the engine heat above the safe point, reduceslubrication, and destroys glow plugs and valves due to high combustion temperature. This is very harmful to theengine and your investment. Learn to tune the engine before flying. Remember, a little rich is always preferredfor long motor life.STARTING PREPARATIONSUse a standard long glow plug. DO NOT USE a R/C or Idle Bar Type plug or Four-cycle plug. Any plug withanything protruding beyond the threads (like the Fox Miracle Plug) will cause damage to the rotary valve.

You will also need a 1.5 volt battery, quality propeller (refer to prop chart) and good commercial grade two cycleglow fuel (yes, two cycle fuel) with 5% nitro-methane (more helps in cold weather). Two cycle fuel contains theright percentage of oil (22%) and be sure the fuels oil contains at least a 50-50 mix of castor oil. Not allsynthetic oil. Keep fuel clean and filter it during fueling. Keep exposure to air to a minimum as methanol willabsorb moisture rapidly.VT 21 VT 49Break-in 8x4; 9x4 10x6; 11x5Normal models 8x4; 8x6; 9x4; 9x5 11x5; 11x6; 12x5Speed models 8x7; 9x6 10x7; 11x7CRANKCASE PRESSURE LINE HOOK-UPMuffler pressure must be connected to head. Vent line on bottom ofcrankcase must be vented to open air. Do not plug this line off.For tank pressure, use "T" between muffler and head or if more pressure isrequired due to poor fuel draw, connect muffler pressure direct to tank andvent both engine lines. Be sure to use fuel with correct oil content.TYPICAL SIDE MOUNTING SHOWNACTUAL STARTINGOpen the high speed needle valve about 4 turns. Your HP four stroke has a built in choke which is actuated byclosing the carburetor barrel completely. This position should be set with your trim in full down position. Chokethe engine and slowly turn the prop over six to ten times counterclockwise. You should see fuel being drawn upthe fuel line. If fuel is not drawn into the carburetor, open the main needle two more turns and unscrew the idleneedle two turns and repeat the above. Don't allow engine to hydraulic lock (this means cylinder filling with fueland piston being unable to compress it). If this occurs, remove glow plug and rotate propeller. Don't force it,serious internal damage can result. Open the carburetor barrel about quarter-way. Connect the 1.5 volt batteryto the glow plug and pull the prop through until you feel a bump before compression. Now the engine will startwith your electric starter.

2> Fuel pick up in tank is not free.3> Dirt or contaminates in the fuel, tank, lines, filter or carburetor.4> Holes in the fuel line. The tear resistance of silicon tubing is very low and it's not uncommon to develop ahole where the fuel line is assembled over the edges of brass tubing. If the engine runs well on the first half oftank and then quits, it's almost always caused by a hole in the pick up line inside the tank. Look for bubbles inthe fuel line, this is also a sign of holes.MAINTENANCEWhen you are finished flying for the day, run your engine dry by removing the fuel line at a moderate speed orallow the fuel tank to run dry. Running the engine dry removes any methanol residue from the internal enginecomponents. This methanol attracts moisture and will result in rust and corrosion if this procedure is notfollowed. It is best to squirt some RJL AFTER RUN OIL in the carburetor, thru lower vent tube and upper oilingtube, then flip the propeller about 10 to 20 times. This oil will keep castor based fuels from gumming and protectinternal engine parts from rust and corrosion. When storing your model between flying sessions, it is best towrap your engine in a rag or plastic to prevent dust, dirt and moisture from entering the engine. The engineshould also be wrapped in a rag at the flying field between flights.If dirt does enter the engine do not turn it over until it has been flushed out completely. Alcohol is recommendedfor this. DO NOT USE carburetor cleaner or chlorinated industrial solvents as they may attack the plastic partsof the engine. The following steps may be used as a disassembly/assemble guide:1> Remove carburetor, intake manifold, exhaust pipe and glow plug.2>Remove the valve cover.3>Remove sliding shims or roller bearing above rotary valve and carefully remove valve.4>Flush engine out completely using alcohol or mild solvent.5>Install and time the valve with piston at top dead center. Insert valve so a equal portion of the rotary valvesport window can be seen thru both intake and exhaust passages in the crankcase casting. If you can't make itexactly equal, the larger opening should be seen thru intake passage. Make sure the piston is at top deadcenter.6> Install valve sliding shims or roller bearing and valve cover with gasket. There should be about .008" to .014"clearance between the cover and valve.7> Install carb, manifold, glow plug and exhaust system.To disassembly/assemble lower crankcase:8> Remove lower crankcase cover, crankshaft, connecting rod, piston/ring, and bevel valve gear.9> Ball bearings are press fitted to the crankshaft and require special tool to remove.10> Clean halves of case with Loctite cleaning solvent to remove factory installed sealant. Do not use a knife orsharp edged tool or sand paper.

11> Install piston/ring on connecting rod and be sure Teflon pads are in place at the ends of wrist pin andretainer shim is on crankpin behind connecting rod. See illustration on previous page.12> Install crankshaft/piston assembly into upper portion of crankcase being sure bearings seat in properlocation.13> Rotate crankshaft so piston is at top dead center.14> Place bevel valve gear in lower case and be sure bevel shaft in secure. Rotate gear so crankpin slot is upand carefully place assembly onto upper crankcase. This is easily done while engine is in the inverted position.Sealant does not need to be used between case halves.15> Re-time valve as described in step 5 above.ENGINE SPECIFICATIONSDisplacementSPECIFICATIONSVT .21 VT 49.21 cu.in.(3.5ccm).49 cu.in(3.5ccm)Bore 0.354 0.898Stroke 0.63 0.772Power .35 hp .75 hpRPMRangePiston/CylType2500 ~15,000Dykes Ringed ABC2500 ~13,000ConventionalRinged ABCWeight 9.5 oz 17.3 oz

ENGINE DIMENSIONSVT 21 VT 49(DIMENSIONS IN MM)A 41.0 54.50B 16.0 22.00C 79.0 100.00D 49.0 63.00E 65.0 81.80F 3.20 4.30G 33.0 42.50

LIMITED WARRANTYYour HP Model Engine has passed rigid factory inspections and is warranted to be free from defects in materialsand workmanship for a period of 90 days, however if you return your warranty card within 10 days from date oforiginal purchase the warranty period will be extended to two years from date of original purchase. Retain yoursales receipt as the as proof of purchase and date of purchase is required.This warranty does no apply to damage caused by:1. Shipping and handling.2. Improper break-in.3. Use of fuel other than specified.4. Crash, misuse or abnormal service.5. Use of muffler or tuned pipe not approved by RJL.6. Any modification, alteration, or abuse of the engine.7. Use for purposes other than engine was designed.8. Use of improper type glow plug.9. Plugging of vent line on bottom of engine.10. Running engine without adequate cooling.11. Use of incorrect size propeller.12. Rusted internal parts.13. Damage caused by hydraulic lock.Other exclusions from warranty are marring or scratching of the finish, any incidental or consequential damagescaused by, or resulting from, a defect in material or workmanship, and normal wear.DO NOT DISASSEMBLE YOUR ENGINE! Doing so will void your warranty. No exceptions! Call us first andexplain your problem.Our liability under this warranty is limited to the repair or replacement of the defect or defective part at ourfactory and does not include inbound shipping expenses. Specifically, no responsibility is assumed for anydamage to any model, accessory, radio control equipment, person or property resulting from a crash in which aRJL or HP model engine is used.WARRANTY CARD MUST BE MAILED WITHIN 10 DAYS OF PURCHASE TO VALIDATE YOUR TWO YEARWARRANTY.Any questions? Call or write: (include your phone number with all correspondence)RJL INDUSTRIES USAPO BOX 5 --- Sierra Madre CA 91025Tel. 626-359-0016

It's easy to time the valve on a HP four strokeThe HP four stroke engines utilize a rotating drum valve in the head rather than conventionalpoppet valves. As the drum rotates the port lines up with the various stages of a four strokecycle: Intake, Compression, Ignition, and Exhaust.

First you must remove the valve cover and the rotating valve. Pay close attention to the shimsand/or bearing located in the valve cover.Find TDC, top dead center (when the piston id at the very top of the stroke). You can place apen down into the cylinder and turn the crankshaft until the piston comes up.

It is easier to mark the prop driver and crankcase at TDC. You may notice a mark on the propdriver from factory assembly. This may or may not be at TDC on your engine because if theprop driver was ever removed it probably wasn't put back on in the same place.Insert the valve with the port window in the rotating valve between the intake and exhaustports.

You should see a small opening of the valve in both the intake and exhaust ports.Yes, both intake and exhaust ports are open at the same time. This is usually referred to asvalve overlap.

Replace all the shims and/or bearings. A new gasket is recommenced and can be purchasedthrough our parts dept.The above information is provided as a guide. Since MECOA/K&B has no way of determining the abilityof the individual using and understanding this information, we assume absolutely NO RESPONSIBILITYfor any damage to person or property from the use of this information.©2004-2006 Model Engine Corporation of America, All rights reserved.MECOA and K&B are Registered Trademarks of Model Engine Corp. of AmericaRegistered U.S. Patent Office

ENGINE CLINICby Clarence Lee

Fifteen years ago, in 1968, Hirtenberger Patronenfabrik of Austria introduced the first commerciallyproduced Schnuerle ported two stroke model engine to the hobby market. Although several individualmodelers here in the U.S. and in Europe had been working with Schnuerle ported engines in U-controlspeed, (Bill Wisniewski, head of K & B’s engine design department and his “Wart” .15 being the mostnotable). Hirtenberger was the first manufacturer to mass produce a Schnuerle ported R/C engine. Thiswas the start of the trend that now finds all high performance two stroke model engines using variousmodifications of the Schnuerle porting. Hirtenberger’s first engine was of .61 Cu. in. displacement andfeatured a rather unusual large diameter drum rear intake. The carburetor being mounted on adownward angle from the bottom of the intake casting did present mounting and fuel tank locationproblems in an R/C aircraft. The engine was a real powerhouse, however. This engine was shortlyfollowed with a more conventional front rotor intake design that became a very popular selling enginehere in the U.S. Over the years, Hirtenberger has expanded their line of engines to include engines from.20 Cu. in. through a 1.20 cu. in. inline twin cylinder engine as well as engines for marine and R/C caruse.This past month I received Hirtenberger’s latest development —a .21 cu. in. displacement four strokeengine. As with Hirtenberger’s original Schnuerle ported engine, they have chosen to depart from thenormal design trend and come up with an entirely different method of four stroke induction. Ratherthan the use of an intake and exhaust valve and the related actuating mechanism, the new HP 21 uses arotating drum or valve mounted vertically in the head with appropriate openings to time the intake andexhaust. The drum valve is driven by a shaft mounted spur gear that is, in turn, driven by a pair of bevelgears mounted in the rear of the crankcase.The master gear in the crankcase is driven by an extension of the crankshaft crankpin. The assemblybeing completely enclosed eliminates the possibility of dirt causing wear to the moving parts andgreatly lessens the possibility of damage due to a crash.Hirtenberger is not the first to market a four stroke engine using a rotary valve type of induction ratherthan poppet valves but their drum valve does differ from the types used by other manufacturers. Webrafirst introduced a rotary valve type four stroke two years ago with their .87 Cu. in. Webra T-4. Thisengine used a variation of the Aspin conical rotary valve used in full size engines. The cone shapedvalve is mounted vertically with the inside of the cone being the head of the combustion chamber. Abelt driven shaft and bevel gearing, in turn, driving the valve. The English Condor 91 also uses ahorizontally mounted cylindrical rotary valve driven directly by a belt on the back of the engine. Boththe Webra T-4 and Condor 91 having their driving mechanism exposed to the elements.Hirtenberger’s new HP 21 is the smallest four stroke engine on the model market. It is a known factthat most four stroke model engines develop about two thirds the power of an equivarent displacementtwo stroke engine but do have the capability of turning larger propellers in the lower rpm ranges. Fourstrokes are also limited in rpm capability by the valve mechanism which has a tendency to “float” atrpm levels much over 10,000. Valve float is simply the point where the valves can no longer open andclose rapidly enough and begin to stay partially open. Increasing the valve spring pressure helps, but, inturn, increases wear to the cam lobes and valve train in general. By going to a rotary valve intakesystem the engine, in turn, has higher rpm capability. Something that would be necessary with a smallerdisplacement four stroke engine. This is the case with the HP 21. One might think that a .21 Cu. in. fourstroke engine might not have enough useful power to be practical. This is far from the truth with the HP21. The Hirtenberger people claim .34 horsepower for the engine at 12,500 rpm. Although not anoutstanding figure for a Schnuerle ported two stroke engine, it is the equal to many of the cross flowported .19’s of just a few years ago.

With the rated horsepower at 12,500, it is obvious that, although of four stroke design, the engine wasnot to be limited to big props and low rpm operation although the engine still has excellent low speedlugging power characteristic of four stroke engines.Over the years, after having run many thousands of engines, I do not really find it one of my favoritefun things to do. The little HP 21 was the first engine to come along in a long time that I was actuallylooking forward to checking out.I received the engine direct from Hirtenberger in Austria with no accompanying correspondence. Justthe instruction booklet printed in four languages. The engine had been run and I imagine it was one ofthe first production line samples. The serial number of #85 would substantiate this. Although the enginehad been run, it seemed to be far from broken-in so I gave it an additional thirty minutes of rich breakinrunning using a 9/6 Top Flite Super M propeller and Cool Power 10% nitro fuel. Although fourstroke engines work better after break-in with lower oil content fuel, I still like 20%-22% oil contentfor the initial break-in while the parts are polishing together and seating. I have also found that whilenitromethane does not give the power increases in a four stroke engine that it does in a two stroke, it isa big aid in the idle and acceleration. I also suspected that as the HP 21 developed its horsepower in the12,500 rpm range, it might benefit by the use of nitromethane.

After the initial rich break-in, rpm/power checks were begun. Cool Power 10% was used for all checksinitially. Actual rpm figures obtained were as follows:7/6 Top Flite, 14,700;8/6 Top Flite, 12,700;9/5 Top Flite,10,800;9/6 Top Flite, 10,200;10/6 Top Flite, 8,200;11/6 Top Flite, 6,500;12/6 Top Flite, 5,600.Needless to say the 11/6 and 12/6 were getting a bit large for the engine but I was curious as to howwell the engine would lug the really big props. The 7/6, on the other hand, was a bit small but, since themanufacturer lists the rpm range of the engine as 2,500-15,000 rpm, I wanted to check the high rpmcapability. When plotting a power graph it is also necessary to run an engine above and below itsmaximum rpm/torque limits to determine its horsepower/torque curve. As can be seen in theaccompanying power graph, the engine had a very flat horsepower peak developing over one thirdhorsepower between 11,000 and 13,000 rpm with a peak of .35 hp at 12,000-12,500. Maximum torqueof 31 oz. in. was obtained at 11,000. Transposed to actual propeller sizes, a 9/6 would appear to be thebest prop for the engine. Allowing for unloading in the air, the engine would turn a little under itsmaximum horsepower peak and slightly above it maximum torque peak. A lot of fellows mistakenlybelieve that an engine should be propped for its maximum horsepower peak, but this would only betrue for all out speed engines. In the case of a sport engine, it is better to run the engine below thehorsepower peak and closer to the torque peak. It is torque that turns the prop and allows the use oflarger propeller sizes. The aircraft naturally plays a part in proper propeller selection, so possibly a 9/5or even 10/4 for an antique scale type model would be more practical. The engine can handle up to an11/6 without overheating if the application should require this size propeller —more on the operatingtemperature later in the article. It is quite interesting to note that Hirtenberger was not overestimatingthe power of the engine and state a horsepower figure actually achieved. I have checked many enginesover the years that claimed horsepower figures considerably higher than those actually obtainable. Ofcourse, many manufacturers resort to “guestimation” rather than by actual dyno testing.The engine was very easy starting and, like most four strokes, liked to start “wet.” Unlike most fourstrokes that seem to start best by flipping backwards - the engine kicks and takes off running in theproper direction - the HP 21 started easiest by flipping in the direction of rotation the same as a twostroke engine. In fact, I could seldom get it to start using the backwards flip start method. Flipping inthe direction of rotation following a wet prime in the exhaust would have the engine running in two orthree flips. Due to the extensive amount of starting and stopping of the engine, I did resort to theelectric starter after the first five or six starts to speed up the testing. A finger over the intake whilehitting with the starter and quickly removing the finger had the engine running in one or two secondsevery time. I. should point out that placement of the carburetor does not make for easy choking of theengine. In fact, there is not enough room between the carburetor intake and top of the front housing foryour finger. However, the carburetor can be rotated in the intake elbow and the elbow, in turn, swung toeither side, then making it an easy matter to choke the engine. The finger manipulation necessary doesleave the thumb sticking towards the prop and you do have to be careful not to get bit as I did a coupleof times.

Throughout the entire testing the engine ran very smoothly and cleanly. There was no trace ofdetonation or tendency for the engine to kick and throw the prop. If the mixture were leanedexcessively, the engine would just stop running.The only blemish on the whole engine performance was the idle. I could not get the engine to idlereliably below 3,500 with 4,000 being a safer figure. This was using the 9/6 prop. Of course, being afour stroke engine with a firing impulse every other stroke, you are getting a 2,000 rpm sound whichmakes the engine seem to be running much slower than it actually is. This was also rather deceiving atthe high end with the engine turning 14,700 rpm, it was hard to believe it was turning this rpm with the7,350 rpm sound.Up until this time I had been using the Cool Power 10% fuel. Being unable to get the engine to idlebelow the 3,500 rpm figure, I now diluted the Cool Power with 50% methanol alcohol giving an oilcontent of 11% and nitro content of 5%. Although the idle did improve very slightly with the drop in oilcontent, it was nothing significant. Power checks were also made with the 9/6 and 8/6 props. Rpm wasdown about 400 indicating the engine did like more nitro. So some fuel was mixed using 10% oil(Klotz), 10% nitromethane, 2% Propylene oxide (an igniter), and the balance alcohol. Rpm was backup to the same as with the Cool Power and idle now improved to the point where it would reliably hold3,500 rpm. With the starting battery connected, it would idle reliably at 2,700. A variety of glow ~plugswere tried including the glow plug that came in the engine, a K & B, Fox, Fireball hot, Glow Bee, andO.S. Four-stroke plug. Plugs did not seem to make that much difference. The O.S. plug seemed to workthe best of all but not that much better over the plug that came in the engine. The Fireball hot didimprove the idle but had a tendency for the engine to misfire at the top end.

I attribute the engine’s non critical plug tendency to the rotary valve drum intake. The glow plug is onlyexposed to the combustion chamber when the port in the drum valve lines up with an opening that leadsto the glow plug; acutally, just about one revolution of the engine. The glow plug being shut off fromthe combustion chamber during the next revolution.Although 3,500 might be a little higher than some fellows might like, it is low enough for mostapplications. If a lower idle is required it might be necessary to use an on-board power supply for theglow plug. Possibly with more running time a lower idle could be achieved. I did accumulate about atotal of two hours running on the engine but it still had a tendency to lose 200-300 rpm after warm-up.That is, starting up from cold, the engine would hit a 200-300 rpm higher figure than after warm-up.Since compression was exceptional and nothing seemed to be tight I would assume that the engine wasstill not fully broken-in.Although the noise level is very low with an open exhaust, the engine does come with a small mufflerthat looks like a small CO2 bottle. As small as the muffler is, it did lower the exhaust levelconsiderably — enough so that you could hear the propeller singing. Surprisingly, the muffler did notcause any loss of power with prop sizes over 8/6. With the 7/6 there was about a 200 rpm drop. Alltesting was done with the muffler installed in order to utilize the muffler pressure for pressurizing thefuel tank. Incidentally, while checking the idle, both muffler pressure and no pressure was tried.

Something I did think was a little strange is the manufacturer’s recommendation for the method ofusing muffler pressure. You will note in the accompanying pictures of the engine that a pressure fittingis installed in the head of the engine. A piece of tubing is connected between this fitting and the mufflerpressure fitting. A line is then run from the crankcase vent fitting on the bottom of the crankcase(between the front and rear bearings) to the tank. Muffler pressure enters the gear box area —passesthrough the hollow shaft that drives the rotary drum valve —through the crankcase and on to the tank.Evidentally, this is done to keep the spur gears in the head lubricated. However, metal particles fromnormal wear, gunk in the crankcase, and a lot of combustion residue from the engine and muffler, areall forced back through the engine and into the fuel tank. With this set-up, a fine screen filter betweenthe fuel tank and carburetor would certainly be a must. Having some real reservations as to thepracticality of this set-up, I chose to take the muffler pressure directly off the muffler fitting as isstandard practice. A shot of oil in the head fitting every half dozen flights should take care oflubrication of the rotary valve spur gears. In fact, I imagine normal fuel leakage past the rotary valvemight provide sufficient lubrication.One of the reasons we can get away with lower oil content fuel in a four stroke engine is due to thelower operating temperature. Firing every other stroke, the incoming fuel charge helps to cool thepiston between firing impulses. Most two stroke glow engines operate with the cylinder head

temperature running between 360o~3800. With a lean run, the temperature can go well into the 400~range. While really lugging the HP 21 down with the 12/6 prop, a cylinder head temperature check wasmade. The engine was running surprisingly cool indicating only 2100 at the glow plug washer and2200 at the exhaust stub. This was with a fully lean, maximum power mixture. Richening the mixturelowered the temperatures by 300. Herein is one of the big advantages of a four stroke engine - lugginglarger props without overheating.The manufacturer lists the bore of the engine as 16.6 mm (.654”) and the stroke as 16 mm (.630) for adisplacement of .21 cu. in. Our particular engine had a bore of .654 but a slightly longer stroke of .638.However, this slight increase in the stroke does not significantly increase the displacement (.212versus .214 cu. in.).The aluminum diecast crankcase/cylinder is a bit unusual in that, rather than being of one piece designwith a removable back plate or back plate and front housing, it splits into two pieces along thecrankshaft centerline. The crankcase half and cylinder head is a one piece unit. This was evidently doneto provide rigidity and maintain proper alignment of the rotary valve drive gearing mechanism. Othermanufacturers have used split crankcase halves in previous years. One example is the late BillAtwood’s Triumph .49 and .51 designs of the late 1940’s. The Atwood Triumph engines also had aremovable front and back plate. Bill Atwood later incorporated this type of crankcase in his CoxConcept .15 and .40 designs that were never put into production by Cox.

With the split crankcase and integral head, I figured the engine would have a chromed cylinder borewithout a separate liner or sleeve. However, this is not the case with the H.P. Close inspection indicatesthat the engine has what appears to be a chrome plated brass sleeve either cast into the casting orpressed in. I could not determine any conventional way of removing the sleeve and did not want to tryforcing things with possible resultant damage. If it were cast in, then there would be no way for itsremoval. There are two holes, approximately 1/8”, drilled 1800 apart in the lower end of the sleevewhich may have been index holes to locate the sleeve while the crankcase was being cast or, possibly,have to do with the installation / withdrawal of the sleeve. As the parts sheet that accompanied theengine does not list a separate sleeve, only the complete cylinder casting, I assume that the sleeve is notremovable.The two crankcase halves do not use a gasket and are assembled with Loctite. This type of splitcrankcase certainly makes bearing installation a snap as you have only to lay the crankshaft/bearingassembly into place and join the two halves together.The integral cylinder head is perfectly flat bottomed in design and the bottom end of the rotary valvefits flush with the inside of the head surface. The piston at top center only clears the bottom of the headby .010” on this engine forcing the air/fuel mixture into the hollow drilled rotary valve. This smallopening is .215” in diameter and approximately .195” deep. So, in effect, the inside of the head surfaceis an extremely wide squish surface forcing the fuel mixture into the small .215” x .195” tubularchamber. The top side wall of the chamber has a .185” square opening that lines up with the exhaustport, intake port, and glow plug port as the rotary valve rotates.Past experience with combustion chamber shapes whould lead me to believe that modification to thissmall tubular combustion chamber shape would result in a power increase. In fact, one of my firstprojects, after RCM’s chief photographer Dick Tichenor gets through taking the photographs toaccompany this article, will be to try a modification to the rotary valve combustion chamber shape. Anextended “Trumphet” shape. Maybe it will result in a power loss but you do not know without trying.The full stroke compression ratio of the engine figures to be approximately 9.77-1. With the smalltubular combustion chamber shape and the glow plug on the side of the head, trying to fill thecombustion chamber with oil to get a volume measurement posed some problems in eliminatingpossible air bubbles.With a two stroke engine, compression ratio is usually figured from the time the exhaust port closes.That is, if an engine has a stroke of .800” and the exhaust port height was .200”, then .600” would beused to compute the compression ratio. In the case of a four stroke engine, the compression strokestarts as the intake port closes which can be anywhere from close to bottom center to 450 after bottomcenter. In the case of the HP 21, the intake closes 350 after bottom center. Actual timing of the HP 21intake opens at 350 before top center and closes 350 after bottom center. The exhaust opens 350 beforebottom center and closes 350 after top center with an overlap period where both the exhaust and intakeare partially open of 700. The intake port closes 350 after bottom center results in a vertical pistontravel of only .040”, hence the reason for the full stroke being used to calculate compression ratio.The piston appears to be a high silicon aluminum, permanent mold casting and uses a Dykes ring. Withthe chrome plated brass sleeve, aluminum piston, and Dykes ring, you might consider the engine ofABCD design — a term first coined by World Engines for some of the Super Tigre line, if I recallcorrectly. The piston is not a lapped or tight fit in the cylinder as with a true ABC design having arunning clearance of .001” and relying on the Dykes ring for sealing. This does make fitting of the

piston/sleeve a somewhat easier task production wise. This particular engine had an exceptionalcompression seal and, until disassembling the engine, I thought it would have a lapped typepiston/sleeve fit. I was quite surprised to find the engine used a Dykes ring. Due to the rotary valveallowing no compression leakage as do regular poppet valves, the engine feels much the same as a twostroke engine with the exception of coming on compression every other stroke.The connecting rod is machined from bar stock aluminum and is of quite massive proportions. Only thebig end is bronze bushed with the wrist pin end running in the aluminum rod. The steel wrist pin is fullfloating and used Nylon pads at the ends rather than what has become pretty universal now — Teflon.Why HP chose to use Nylon is a bit puzzling but they evidently felt that, due to the lower operatingtemperature, Teflon would not be required.The crankshaft is made of steel, hardened, and finish ground on the bearing surfaces. The crankpin is aseparate pressed-in piece and presses into a very massive crank disc that is .195” wide. The crank discis, in turn, milled on each side of the crankpin to provide counter balance. A small extension on the endof the crankpin drives a bevel gear that meshes with the mating bevel gear that, in turn, drives a shaftand the spur gear rotary valve in the head. The crankshaft is supported by two ball bearings of Japanesemanufacture. The rear bearing is 24 mm (.945”) O.D. x 9 mm (.354”) I.D. and the front bearing is 19mm O.D. (.748”) x 7 mm (.275”) I.D. The front bearing is of the double sealed type to keep foreignmatter from entering and, in turn, sealing the crankcase.The carburetor is of the rotating barrel type that moves in and out as it rotates. An idle mixtureadjustment is provided on one side and the high speed mixture adjustment on the opposite side. Thecarburetor venturi diameter appears quite small at .160” (after working with two stroke carburetors forso many years), but one must remember that four stroke engines have much longer intake and exhaustperiods so that large intake and exhaust openings, as used on two stroke engines, are not required.As can be seen from the accompanying photographs, the HP 21 is of rugged construction and, in myopinion, has a very nice overall appearance. The down sloping intake tube with the inverted carburetordoes account for a rather different look. The intake manifold can be removed and the carburetormounted directly to the head if a particular application that would require this type of mounting shouldarise.Four stroke engines certainly seem to be the coming thing judging by all the manufacturers that arenow producing them. In the quest for more power, I believe more manufacturers will be turning torotary valve type designs to overcome the rpm limitations of poppet valves. As with their original HP .61 Schnuerle engine that started the present trend to high performance two stroke engines, the HP 21four stroke and its big brother the HP 49 not yet released at the time of this writing, has lead the waywith the first of what might be considered “high speed” four stroke engines.The engine is being imported into the U.S. by Tower Hobbies and will sell for a very low $79.98. Thisis the lowest price four-stroke on the market.All Contents Copyright © 1983. R/C Modeler Corporation. All Rights Reserved.